The king (the official term used in the constitution, even though all monarchs since 1890 have been female.)
Has this merely been a result of coincidence? No male children born to the Dutch Royal Family, or the eldest has always been a daughter? Or, something quirky about those very lovable Dutch people? "Look Daddy, I--" "Don't say anything. Sit down." "Look here, let's try to forget this. If you promise--" -- Song of Solomon, CW